Device for promoting the removal of water from a paper-making pulp slurry



Nov. 7, 1967 w DUNCAN 3,351,524

DEVICE FOR PROMOTING THE REMOVAL OF WATER FROM A PAPER-MAKING PULP SLURRY Filed Dec. 51, 1964 W fl, DONG/9A1 I N VEN TOR.

United States Patent 3,351,524 DE"ICE FOR PROMOTENG THE REMOVAL,

GI WATER FROM A PAPER-MAKING PULP SLURRY William A. Duncan, Toronto, Untario, Canada, assignor to Union (Iariside Canada Limited, Toronto, Ontario, Canada, a company of Canada Filed Dec. 31, 1964, Ser. No. 422,786 6 Claims. (Cl. 162-374) ABSTRACT OF THE DISULOSURE A suction box cover having a relatively hard smooth flat screen contacting surface which comprises a smooth surfaced base member, a metal sheet of a thickness between inch and A2 inch bonded to said surface and a ceramic coating of a hardness of at least 7 on the Mohs scale bonded to the exposed surface of the metal sheet.

This invention relates to devices for promoting the removal of Water from a paper-making pulp slurry supported on the wire screen of a paper-making machine. More particularly, this invention relates to new and improved suction box covers and hydrofoils.

Suction boxes or hydrofoils are used in the paper-making industry for the purpose of removing water from the paper-making pulp slurry which is deposited from the head-box of a paper machine onto the Fourdrinier wire thereof. The moving wire carrying the pulp slurry passes over the suction boxes or hydrofoils, which actually engage the under-surface of the wire, and which draw water from the pulp slurry through the wire. Suction boxes, per se, are well known in the art and have been used for many years. Hydrofoils are discussed at some length in United States Patents 2,928,465 dated Mar. 15, 1960, P. E. Wrist, and 2,928,466 dated Mar. 15, 1960, G. Burkhard et al.

For many years suction box covers were made of end grain maple. These relatively soft covers have proven to be unsatisfactory, since they become embedded eventually with grindstone grit suspended in the wood pulp. This materially increases the wearing effect of the suction box covers on the Fourdrinier wire, which, during operation, is in intimate frictional engagement with the suction box covers, thereby decreasing the life of the wire. Fourdrinier wires are very expensive, and for this reason and others, such as lost production and the labour involved in replacing a wire, it is extremely desirable to prolong the life of a Fourdn'nier Wire for as long as possible.

Certain steps have been taken in the past to meet this objective. Thus a solid silicon carbide suction box cover has been designed and successfully operated. In addition, metal suction box covers having the Wearing surface thereof coated with materials such as tungsten carbide have been proven to be successful in meeting this objective, as have two-part suction box covers consisting of a base member fabricated from steel, or the like, to which has been bonded a plate formed of solid silicon carbide or some other suitable ceramic material.

While all of the foregoing types of suction box covers can be used with a marked increase in wire life, unfortunately each type of suction box cover suffers inherent disadvantages, the relatively high cost of manufacture being a disadvantage of all of the foregoing types.

In the case of a suction box cover which either consists of a plate of ceramic material, such as silicon carbide, alone or bonded to a base material such as steel, considerable difiiculty has been experienced in finishing the wearing surface of the plate to make a smooth flat surface, this being because of the hardness of the ceramic plate, of

course. In the case of suction box covers which consist of a base member such as stainless steel, for example, usually about /2" thick and coated with a ceramic material such as tungsten carbide, for example, it is difficult to manufacture a stainless steel base member having a perfectly flat surface, and the high temperature processes employed to coat the base member with ceramic material tend to distort the base member, which necessitates further flattening of the coated base member. Even after flattening of the coated member has been effected, it will be appreciated that if the surface of the base member to be coated was not flat initially, there will be high spots in the coating which will receive maximum wear, even to the extent, in some cases, of penetration of the coating.

In accordance with this invention a hydrofoil or suction box cover is fabricated from a base member and a thin metal sheet which has a ceramic coating on one surface thereof. The base member preferably is a fabric base, phenolic impregnated high pressure laminate. The base member therefore has a hard surface, but a surface which can be finished to a high degree of smoothness much more readily than the surface of a comparable stainless steel plate of say /2" in thickness. The thin metal plate preferably is fabricated of stainless steel and is less than about Ms" in thickness. These two components are bonded together by a suitable adhesive in an accurate press, which results in the coated surface of the metal sheet being more nearly flat after the metal sheet has been bonded to the base member, because inequalities in the coated surface will be pressed out. Such a hydrofoil or suction box cover has a coated surface which can be finished faster than the other prior art types of suction box covers mentioned herein, because less metal is required to be removed.

In addition, it is much simpler to drill through such a suction box cover than through a plate of stainless steel of comparable thickness. Furthermore, the cost of materials for such a suction box cover or hydrofoil is less than for such a device fabricated entirely from stainless steel and of comparable size.

This invention will become more apparent from the following detailed description taken in conjunction with the appended drawings, in which:

FIGURE 1 is a perspective view of a suction box cover embodying this invention,

FIGURE 2 is a section taken along line 22 in FIG- URE 1, and

FIGURE 3 is a section through a hydro-foil embodying this invention.

Referring to FIGURES 1 and 2, there is shown a suction box cover 10 which consists of a base member 11 and a thin metal sheet 12 which is bonded to the upper surface 13 of base member 11. A plurality of apertures 14 are drilled through cover 10, and, in accordance with conventional practice, are bevelled at 15 to avoid excessive wire wear or damage caused by the suction depressing the Fourdrinier wire slightly into openings 14 as the wire travels over the suction box cover.

In FIGURE 3 there is shown a hydrofoil 20 embodying this invention. As in the case of suction box cover 10, hydrofoil 20 consists of a base member 11 and a thin metal sheet 12 which is bonded to the upper surface 13 of base member 11. Unlike suction box cover 10, however, no apertures are drilled in hydrofoil 20. In addition, it will be noted that metal sheet 12 is shown to be bonded only to the leading part 21 of hydrofoil 2t), i.e., the lead ing part being the princical part on which the wire travels, the trailing part 22 of hydrofoil 20 consisting usually only of base member 11. Furthermore, while upper surface 13 of base member 11 of cover 10 is planar, upper surface 13 of base member 11 of hydrofoil 20 lies in two planes as at 13 and 13a which inersect at an obtuse angle along a line 23. It will be appreciated, of course, that FIG- URE 3 is somewhat schematic in nature, and reference is made to the aforementioned patents for a more detailed description of hydrofoils.

In accordance with this invention, base member 11, which is usually about /2" thick, is fabricated from a material which can be readily drilled, which can be readily finished, as by lapping, for example, and which has a hard surface 13 that will resist deformation when metal sheet 12 is bonded thereto in a press. Preferably base member 11 consists of a fabric base, resin impregnated high pressure laminate formed by bonding together under pressure a plurality of layers of fibrous sheet material impregnated with any suitable heat-hardenable resin such as a phenolic or an epoxy resin, for example. In less preferred embodiments of this invention base member 11 may be fabricated from a hard wood or even from a suitable metal such as stainless steel, for example, that will resist the corrosive conditions which will be encountered in use in a paper mill.

Metal sheet 12 preferably is stainless steel, but other metals such as aluminum, brass, bronze or copper, for example, which will resist corrosive attack under paper mill operating conditions could be substituted therefor. Preferably metal sheet 12 is not more than about thick.

The wearing surface 16 of metal sheet 12 which is smooth and flat is coated with an impermeable ceramic material which has a hardness on Mohs scale of at least seven. A number of ceramic materials may be employed. Thus, for example, the coating may be any one of the following or any mixture thereof: tungsten carbide, chromium carbide, titanium carbide, zirconium carbide, boron carbide, silicon carbide, chromium oxide, titanium boride, zirconium boride, titanium nitride, zirconia and alumina.

The coating may be applied to wearing surface 16 by a number of conventional methods. Thus the Plasmarc (Trademark) plating technique as described in one or more of United States Patents 2,802,093; 2,806,124; 2,847,555; 2,858,411; 2,858,4122; 2,862,099; 2,868,950; 2,871,336; and 2,874,265 or the Flame-Plating (Trademark) technique as described in United States Patent 2,714,563 may be employed. It will be aprpeciated, of course, that the coating, which generally will be of the order to 20 thousandths of an inch in thickness, is applied only to wearing surface 16.

In manufacturing a suction box cover 10 or hydrofoil 20 embodying this invention, surface 13 is lapped or otherwise finished to make the surface smooth, flat and uniform. Any suitable adhesive or bonding agent such as an epoxy or phenoxy resin, for example, then is applied preferably to both surface 13 and the undersurface 17 or uncoated surface of sheet 12. Metal sheet 12 then is placed against base member 11 with surfaces 13 and 17 together, and the assembly is placed in an accurate press where these two components are bonded together under the influence of heat and pressure. Because of the thinness of metal sheet 12 and the fact that it is fabricated from a metal such as stainless steel, rather than from a solid hard ceramic material, any irregularities in the sheet tend to be pressed out during this step.

Once the bonding operation has been completed, surface 16 is finished by conventional techniques, such as lapping, to a smooth, fiat, low friction surface of a hard, impermeable ceramic material. This step may precede the step of bonding metal sheet 12 to base member 11 if desired, but is more advantageously carried out following the bonding operation.

In the case of a suction box cover 10 which requires openings 14, these may be drilled after the bonding step and before the lapping step. However, it also is possible to drill both base member 11 and metal sheet 12 separately, in which event it is desirable to drill sheet 12 before the coating is applied to wearing surface 16 thereof. Depending upon the thickness of metal sheet 12 and its composition, it may be possible to punch openings 14 therein rather than drill the same, and this may avoid a separate machining step to provide bevels 15.

It will be appreciated that after a suction box cover or hydrofoil embodying this invention has been in service for some time, a new coating may be applied to wearing surface 16, or the whole sheet may be peeled off of base member 11 and replaced.

While preferred embodiments of this invention have been described herein, those skilled in the art will appreciate that changes and modifications may be made therein without departing from the spirit and scope of this invention as defined in the appended claims.

What I claim as my invention is:

1. A suction box cover for a paper-making machine which comprises a base member having a smooth surface, a metal sheet having a thickness of between inch and Vs inch bonded to said smooth surface. A ceramic coating bonded to the exposed surface of said metal sheet to form a screen contacting surface portion; said coating having a hardness of at least 7 on Mohs scale.

2. A cover as in claim 1 wherein the base member is a fabric base phenolic impregnated high pressure laminate.

3. A cover as in claim 2 wherein said metal sheet is stainless steel.

4. A cover as in claim 3 wherein the ceramic coating is one selected from the group consisting of tungsten carbide, chromium carbide, chromium oxide, titanium carbide, zirconium carbide, boron carbide, titanium boride, titanium nitride, zirconium boride, zirconia, alumina and silicon carbide.

5. A suction box cover for a paper-making machine which comprises a base member consisting of a fabric base resin impregnated high pressure laminate having a smooth surface, a stainless steel sheet having a thickness of between A inch and 4; inch bonded to said smooth surface, a tungsten carbide coating bonded to the exposed surface of said metal sheet, said coating having a hardness of at least 7 0n Mohs scale.

6. A cover as in claim 5 wherein the bonding means bonding said stainless steel to said smooth surface is selected from the class consisting of epoxy and phenoxy resins.

References Cited UNITED STATES PATENTS 12/1962 Gould 162374 7/1963 Taylor 162374 

1. A SUCTION BOX COVER FOR A PAPER-MAKING MACHINE WHICH COMPRISES A BASE MEMBER HAVING A SMOOTH SURFACE, A METAL SHEET HAVING A THICKNESS OF BETWEEN 1/16 INCH AND 1/8 INCH BONDED TO SAID SMOOTH SURFACE. A CERAMIC COATING BONDED TO THE EXPOSED SURFACE OF SAID METAL SHEET TO FORM A SCREEN CONTACTING SURFACE PORTION; SAID COATING HAVING A HARDNESS OF AT LEAST 7 ON MOH''S SCALE. 